Exoplanet Observing using AstroImageJ · eff: 6300 6 V mag: 11.7 Suggested range of comp stars:...

Exoplanet Observing UsingAstroImageJ

Dennis M. ContiChair, AAVSO Exoplanet Section

© Copyright Dennis M. Conti 2017 1

AstroImageJ (AIJ)

• All-in-one freeware developed and maintainedby Dr. Karen Collins

• Can be used for image calibration, differential photometry, exoplanet transit modeling

• Latest version can be found at:http://www.astro.louisville.edu/software/astroimagej/

• A step-by-step guide to using AIJ for exoplanet observing can be found in “A Practical Guide to Exoplanet Observing” at:http://astrodennis.com


Worksheet


Exoplanet: WASP-12b

Observer: Dennis Conti

Item Host Star/Exoplanet Information: (click here)

1 RA: 06:30:32.79

2 Dec: 29:40:20.4

3 Period (days): 1.0914

4 R*: 1.63

5 T eff : 6300

6 V mag: 11.7

Suggested range of comp stars: 11.26 to 12.45 mag

7 Link to Reference Paper (optional): https://arxiv.org/abs/1512.00464

8 Date of Observation (UT): 01/5-6/2016

BJD_TDB

9 Predicted Ingress: 2457393.53948

10 Predicted Egress: 2457393.66431

Predicted midpoint: 2457393.60190

11 Model fit midpoint (Tc) in BJD_TDB: 2457393.60123

Approximate difference: 1.0 minutes

Observing Location:

12 Latitude: 38:55:48.51 N

13 Longitude: 76:29:17.78 W

14 Altitude (m): 0

15 Aperture (mm): 280

16 Focal length (mm): 3010

17 Make/model of CCD Camera: SX694M

18 Gain (e-/ADU): 0.3

19 Readout noise (e-): 5.0

20 Dark current (e-/pixel/sec): 0.003

21 Point of where CCD goes non-linear (ADUs): 45,000

X Y

22 No. of pixels (unbinned): 2750 2200

23 Pixel size (microns -unbinned): 4.54 4.54

24 Binning used for this observation: 2 2

25 Exposure time (secs): 45

26 Filter used: V

Limb darkening coefficients: (click here)

27 Quadratic LD u1: 0.39056081

28 Quadratic LD u2: 0.3026992

Image scale (arcsec/pixel): 0.62 0.62

FOV (arcmin): 14.26 11.41

29 FWHM (arcseconds): 2.68

FWHM (pixels): 4

Initial Settings:

30 FWHM pixel multiplier: 3

Aperture radius: 13

31 Inner annulus radius: 14

Outer annulus radius: 29

Final Settings:

32 Aperture radius: 13

33 Inner annulus radius: 14

34 Outer annulus radius: 29

# of Science Images:

35 Original #: 336 Final #: 336

36 Images not used:

AIJ Pipeline


Raw Bias, Dark, Flat Files Raw Science Images

DP(CCD Data Processing Function)

• Create master bias, dark, flat calibration files• Calibrate Science images and optionally add

FITS fields (e.g., BJD_TDB)

pipelineout_ files

cont’d

AIJ Pipeline (cont’d)


pipelineout_files

Image Analysis

• Determine FWHM and initial Aperture/Annulus radii using Alt-Left Click on target star

• Align images if necessary using Align Stack tool• Eliminate “bad images”• Select appropriate comp stars

cont’d



Multi-Aperture Photometry

• Aperture settings: Aperture/Annulus radii CCD gain, readout noise, dark current Saturation and linearity warning levels

• Place apertures• When photometry completed, save

Measurements table

cont’d

Important AIJ Terms

• T1: refers to target star

• Ci: refers to comparison star

• Source-Sky_xx: ADU counts in the aperture for star xx after the sky background is taken out (e.g., Source-Sky_C2)

• tot_C_cnts: the sum of the Source-Sky counts for all the comparison stars

• rel_flux_T1: the relative flux of target star T1= Source-Sky_T1/tot_C_cnts

• rel_flux_Ci: the relative flux of comp star Ci= Source-Sky_Ci/total cnts of all other C stars


AIJ Plotting

• Uses a plot configuration file with an extension of .plotcfg

• A sample plot configuration file,Measurements_Template.plotcfg,can be downloaded from http://astrodennis.com




Multi-plot Main Screen

• Select BJD_TDB timebase in Default X-data• Fill-in Title and Subtitle• Fill-in Left and Right values for Fit and Normalize Regions

(i.e., predicted ingress/egress times); copy them toV. Marker 1 and V. Marker 2

• Select Auto X Range and click on arrow• If a meridian flip occurred during transit, click on Show

and enter Flip Time

cont’d



cont’d

Multi-plot Y Data Screen

• Plot AIRMASS vs. tot_C_cnts: will show changes in sky transparency• Plot Source-Sky counts for target and comp stars: will show those

with too much scatter• Plot rel_flux of comp stars: will show those that might be variable; deselect

those that are variable using the Multi-plot Reference Star Settings screen• Plot rel_flux of target and its transit fit



Data Set 2 Fit Screen

• Enter predicted period• Enter target star radius (R*)• Enter predicted inclination (don’t lock it)• Enter limb darkening coefficients (u1 and u2) and lock them

cont’d



Data Set 2 Fit Screen

• If a meridian flip occurred during transit, select Meridian Flip as a detrendparameter

• Set detrend parameters (at most 3) that result in a reduction in BIC by morethan 5 (start with AIRMASS)

• Sequentially deselect comp stars until a minimum RMS is obtained• See “A Practical Guide to Exoplanet Observing” for further

optimization guidelines and how to create a dataset for input to external programs

Exoplanet Observing using AstroImageJ · eff: 6300 6 V mag: 11.7 Suggested range of comp stars:...

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